The use of road deicing salts has tripled in the U.S. over the last 45 years, posing an increasing threat to human health and the environment as they wash into drinking water sources, a new study warns.
The new research from The University of Toledo in Ohio, entitled “Road Salts, Human Safety and the Rising Salinity of Our Fresh Waters,” considers the balance between keeping drivers safe on icy winter roads and mitigating the negative environmental and health impacts triggered by dumping salt on streets.
In terms of magnitude, the study notes that snow and ice are issues for as many as 70% of U.S. roads. The use of salt deicers has reduced as many as 87% of potential vehicle accidents since the practice began in 1938. To make this possible, U.S. road crews dump a remarkable 25 million metric tons of sodium chloride each year.
While the U.S. rate is high, the study takes note of Canadian provinces such as Ontario, Quebec and Alberta, which often have even higher rates of salt use, reaching as much as 11 kg/m² of highway.
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The study found that in areas where they are used, deicing salts become the primary anthropogenic contributor to high chloride concentrations in freshwater systems.
In one glaring instance, the researchers report that overuse of road salts likely contributed to higher levels of corrosive chloride in the water supply in Flint, Michigan, in 2014, leading to the release of lead from water distribution pipes.
The research out of the UToledo Lake Erie Center also highlights that some urban streams have salt concentrations that are 20 to 30 times higher than the Environmental Protection Agency’s chronic chloride threshold of 230 milligrams per litre.
“Current EPA thresholds are clearly not enough,” announced Dr. Bill Hintz, assistant professor of ecology at UToledo and lead author of the research, in a statement. “The impacts of deicing salts can be sublethal or lethal at current thresholds and recent research suggests that negative effects can occur at levels far below these thresholds,” he added, noting that federal limits to protect fish, plants and other aquatic life in freshwater ecosystems are commonly surpassed.
Hintz, who collaborated with scientists from Montana State University and Rensselaer Polytechnic Institute on the study, said that the most common deicers are inorganic salts like sodium chloride, calcium chloride and magnesium chloride, all used in solid and liquid or brine form.
The EPA’s drinking water threshold for chloride can also be exceeded when salt contamination has occurred, the study found, leaving private wells particularly vulnerable.
In terms of recommendations, the UToledo study suggests the use of live-edge snow plows instead of conventional single fixed-edge plows. The former uses springs that help the blades conform to the convex shape of the road, allowing for a closer plow.
Environment and Climate Change Canada has compiled some interesting case studies to illustrate alternatives to the use of standard road salt, such as anti-icing and pre-wetting techniques used in Vancouver ski resorts, which are options that are also explored in the new UToledo study.